This invention relates to indicator means for an absorbent pad assembly, and particularly disposable diapers, which visually signals the user when the pad is wetted by aqueous fluids to assist the user in determining whether or not a fresh pad is needed.
In the prior art a number of such indicators are disclosed for that purpose. However all of these rely on systems wherein the indicator is initially not visible or is temporarily masked. These prior art indicators become visible only after the pad is wetted.
For example, Baker et al U.S. Pat. No. 3,675,654 of July 11, 1972 utilizes an indicator agent which is disposed between a translucent backing sheet and an absorbent pad and comprises either a small amount of finely divided water-soluble dye having a high dye strength of such a dye admixed with a finely divided diluent masking agent such as talcum powder. The indicating agent is applied in dry form and adheres to the pad surface facing the backing sheet where it is substantially invisible through the backing sheet. When the pad and the agent becomes wet from an aqueous body fluid the dye becomes visible through the backing sheet.
Wang U.S. Pat. No. 3,759,261 of Sept. 18, 1973 utilizes an internal layer carrying a printed pattern which is covered by another layer of sufficient density to conceal the printed pattern when the diaper is dry but which when wetted permits the printed pattern to become readily visible.
While each of these perform the desired function of indicating diaper wetness, it was found that some mothers were not in favor of using a system because is also signalled to everyone else that their child was wet and needed changing. A more discreet, less conspicuous means for indicating wetness appeared desirable.
The present invention utilizes such an approach. It provides a wetness indicator while the diaper is dry shows a decorative color or printed pattern through the backing sheet. When a diaper is wetted this color or pattern quickly fades and then substantially disappears from view.
The principle employed in the invention is similar to one found in Sheppard et al U.S. Pat. No. 3,702,610 of Nov. 14, 1972 which teaches the use of a colored water-dispersible adhesive binder for non-woven wrappers which when dropped in the excess water of a toilet is gradually dissolved and dispersed by the water whereby the color migrates away from the bonded areas into adjacent unbonded areas to indicate that the bonded areas are dissolved and that the wrapper is ready for flushing. However, the Sheppard et al indicator system is used for an entirely different function and purpose than that which will be defined herein.